Unregulated Power PCB

[luvdunhill]

I have a few uses for a simple, regulated power PCB that supports a number of different ~25VA PCB mount transformers with a bit of filtering on each side of the transformer. I'm trying to nail down the schematic a bit and wanted to see if there was any advice out there

[n_maher]

Your title says unregulated, the text says regulated, to my untrained eye the schematic appears to show an unregulated supply but I wouldn't swear to it.

[luvdunhill]

yeah, oops. let's say "filtered" or CLRC? heh..

[digger945]

I like it. You thinking about making it so you can use 2 regular supplies or bi?(user configurable)(maybe a prefab bridge, and flip 180 for desired polarity)

Edited September 5, 2010 by digger945

[MASantos]

Why the need for unregulated power supply? A simple LM78XX or LM317 wouldn't add much to the price or complexity.

[luvdunhill]

I like it. You thinking about making it so you can use 2 regular supplies or bi?(user configurable)(maybe a prefab bridge, and flip 180 for desired polarity)

So, the options would be single voltage with secondaries in series, single voltage with secondaries in parallel, or dual voltage... Should I worry about polarity?

No regulator, as the idea is that putting it here will be inferior to having it right next to the circuit. Also, plenty of uses where this is enough, like digital or maybe even where a CCS is employed to isolate the rails on the main boards.

[digger945]

... Should I worry about polarity?

Nope. Just saying that the way your schematic is drawn you could possibly use it either way(which I think is handy because some older stuff requires a negative supply).

I'm guessing you will go "fail safe" and use diodes so it could be configured either way, and allow the diode of your choice.

No regulator, as the idea is that putting it here will be inferior to having it right next to the circuit. Also, plenty of uses where this is enough, like digital or maybe even where a CCS is employed to isolate the rails on the main boards.

Right.

btw, what you have from the wall to the tranny is almost identical to what I'm working on for an unregulated HV supply. Actually the whole thing is pretty close, except for the inductors after the rectifier. Never seen that before. Would you care to give some hints as to what's going on there?

EDIT: Aha. nvm I see now. Very clever.

Edited September 5, 2010 by digger945

[luvdunhill]

ah I see why I was confused, I have an error. heh. The bottom supply is the negative supply but the bridge is not drawn right. So, you think people might want two positive supplies or two negative supplies? This would probably mean that I couldn't use a common ground plane. edit: oooh you're talking about a single negative supply, right? yeah, finally catching up with you, that would indeed be cool, but that doesn't require flipping... (I think) just use the bottom circuit and jumper the secondaries properly.

I'll going to be supporting a SMD Schottky bridge and probably TO-220 type diodes. The bridge (610-CBRHDSH2-100TR13) isn't really flippable (but a very cool part), so I'll have to figure out if that will require special care.

Edited September 5, 2010 by luvdunhill

[MASantos]

What's the purpose of the inductors after the rectifier?

Scott share your findings!!

Edited September 5, 2010 by MASantos
correct some spelling

[luvdunhill]

What's the purpose of the inductors after the rectifier?

Scott share your findings!!

It helps smooth the supply and/or isolates the ground. In the end this can be either an inductor (common mode or choke) or a resistor.

[digger945]

Are the two halves of the inductor for one supply line wound on the same core?

Manuel, it helps to resist changes in the supply line by storing energy in the form of a magnetic field. As the current or voltage change the field changes, and will help to absorb or release energy as needed. This, provided the right inductor and core. Frequency is another factor.

[voodoochile]

That looks like it would run pretty smooth; have you modeled it?

I like it.

[nikongod]

ah I see why I was confused, I have an error. heh. The bottom supply is the negative supply but the bridge is not drawn right. So, you think people might want two positive supplies or two negative supplies?

I think that if you put a few jumpers on the board the user could select whether this was a ++, +-, - - board.

Also, the secondaries of the transformer arent hooked up to the bridge on both ends. Was this Intentional?

[luvdunhill]

ok, even with copious amounts of beer, I don't get it. Why does it matter how the outputs are connected? Why do you need jumpers? It's a center-tapped output, so you can reference things however you want (++, +-, --). Perhaps the only consideration I can think of is how the ground plane is oriented... am I confused?

Ari, yeah, the secondaries aren't connected so you have the option of 1 supply with 2V, 1 supply with 2I, or 2 supplies with separate secondaries,

I have modeled it. The key is finding proper parts now. I'm looking at the path current compensated choke for the input side, like this:

http://www.schaffner.com/components/en/_pdf/Datasheet%20RN_series%20e18.pdf

I need 47-100mH here on the input side.

On the output side, I'm still playing with the numbers. Yeah, they're typically wound on the same core, like this:

[luvdunhill]

has anyone ever used or considered a resettable thermal breaker in lieu of a fuse? Seems like they might sound better than a fuse ... ahem.

[MASantos]

Seems like they might sound better than a fuse ... ahem.

[luvdunhill]

I sorta want to posit such a claim in the fuse-douche thread at HF and see what happens... thermal breakers and PTCs perhaps.

[MASantos]

I sorta want to posit such a claim in the fuse-douche thread at HF and see what happens... thermal breakers and PTCs perhaps.

Dew it!!

[luvdunhill]

update

[luvdunhill]

Dew it!!

done

[luvdunhill]

oops... update:

edit: FWCT note doesn't work

Edited September 7, 2010 by luvdunhill

[luvdunhill]

fixed:

[MASantos]

Those are varistors on the primary right?

[luvdunhill]

Those are varistors on the primary right?

Yes, MOVs. The downstream components are optimized for small spikes, not medium to large ones...

[MASantos]

That's a nice touch, most AC filters and filtered IEC's don't have surge protection and they should. I have some industry around my place and the voltage tends to go north of 250v from time to time, quite a helpful part!